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fails Apple Hardware Test: 2I2C error

I have a 20" 1.8GHz iMac G5 from late 2004.

It was having general instability problems so I tried putting a clean reinstall of the OS, but the process failed, three times in a row. So I ran the AHT disk which came with the machine, and it quickly failed the short test with the following error code:


Sounds like it could be related to the I2C bus to me. However, the I2C system is mainly diagnostic and reporting in nature. It reports actual voltage levels on the ram cards and PCI slots, stuff like that. So possibly, this error may not be the real problem.

I took the machine in to an Apple store and one of the techs noticed and showed me there was a bulging capacitor. Since they can only replace the whole board and send the old one back for remanufacturing (expensive), I wanted to try to fix it myself.

After reading about the capacitor/power supply problems I got a new power supply and worked on identifying the capacitor and finding its specks. I learned that beyond the capacitive value, voltage, and temperature ratings; that there are three related charateristics which seem to be critical to the power filtering role these capacitors play in this machine. (impedance or Z)^2 = (equivalent resistance or ESR)^2 + (capacitive reactance or X)^2 If you know two of them you can compute the third. Typically ESR is small and Z ~= X.

So why is this relevant? Well, the original capacitors are Chemi-Con KZJ Ultra Low impedance line with a Z = 12.5 m Ohms @ 100 kHz, unfortunately, this line was discontinued. Chemi-Con current offerings have impedances which range from 22 m Ohm to 49 m Ohm. Nowhere near the original spec. Worse, Digi-Key and Mouser don't carry the better lines, not even in a quantity of one! So I ordered the best available. When it arrived, I removed the bulging capacitor and soldered the new one into place. I also swapped out the power supply. Restarted the machine and... exactly the same problem as before. It still doesn't pass AHT, same error message.

So, does anyone on here have some advice on what I should try next?

Sorry about the long explanation, but hopefully it explains why I'm finding the whole thing puzzling. Why does Chemi-Con no longer manufacture capacitors with such low impedance any more? Why doesn't DigiKey carry what they do offer?

Answer this question I have this problem too

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2I2C/1/1: 0x00000092 error code is that the thermal sensor of the hard drive is bad or unplugged...

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I'd say it's quite possible that no one manufactures the specific capacitor now since the latest tech doesn't utilize it. My only suggestion is that you buy an otherwise broken motherboard and salvage the capacitor. No idea how much broken g5 logic boards go for, probably not much, but if you want to keep costs down you can find other more generic boards using that capacitor and steal the capacitor from one of those.

Good luck

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A capacitor can fail even if it still physically looks good. Assuming that your replacement capacitor was of acceptable low ESR, other capacitors of similar brand and capacity (typically those more than 1000 ufd capacity) should also be suspected and replaced. Heat and age degrade capacitor function like nothing else.

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My first iMac G5 20" had its logic board replaced already within its first year, 2006, under guarantee, then in 2012 this error code resulted from running the AHT. The machine finally failed to work at all. Not too keen on spending about 1,000 euros on repair, I bought an older, used iMac G5 20" in 2013. It too had had its logic board replaced within its first year. It worked well for over a year, but now, in July 2015, its logic board has failed again. So both my iMac G5s are useless!

Having read all the previous posts, the cause seems to remain a mystery. Has anyone identified the real fault with this logic board? Is it the capacitor? Or is the fault in the thermal sensor of the hard drive, as carol godbout above says? Or some other component?

This computer has some very desirable features, especially for running Classic applications. Fortunately, there are several firms who can repair the logic board, so they must know what the problem is. However, my local Apple-authorised agents here in France refuse to consider repairs!

The shame is that Apple must have known about these many failures but took no corrective action.

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ciradrak will be eternally grateful.
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